Multi-mode integrated starter-generator device with dog clutch arrangement

ABSTRACT

A combination starter-generator device is provided for a work vehicle having an engine. The starter-generator device includes an electric machine; a gear set configured to receive rotational input from the electric machine and from the engine and to couple the electric machine and the engine in a first power flow direction and a second power flow direction. The gear set is configured to operate in one of at least a first gear ratio, a second gear ratio, or a third gear ratio in the first power flow direction and at least a fourth gear ratio in the second power flow direction. The starter-generator device further includes a dog clutch arrangement selectively coupled to the gear set to effect the first, second, and third gear ratios in the first power flow direction and the fourth gear ratio in the second power flow direction.

CROSS-REFERENCE TO RELATED APPLICATION(S)

Not applicable.

STATEMENT OF FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

FIELD OF THE DISCLOSURE

This disclosure relates to work vehicle power systems, includingarrangements for starting mechanical power equipment and generatingelectric power therefrom.

BACKGROUND OF THE DISCLOSURE

Work vehicles, such as those used in the agriculture, construction andforestry industries, and other conventional vehicles may be powered byan internal combustion engine (e.g., a diesel engine), although it isbecoming more common for mixed power sources (e.g., engines and electricmotors) to be employed. In any case, engines remain the primary powersources of work vehicles and require mechanical input from a starter toinitiate rotation of the crankshaft and reciprocation of the pistonswithin the cylinders. Torque demands for starting an engine are high,particularly so for large diesel engines common in heavy-duty machines.

Work vehicles additionally include subsystems that require electricpower. To power these subsystems of the work vehicle, a portion of theengine power may be harnessed using an alternator or a generator togenerate AC or DC power. The battery of the work vehicle is then chargedby inverting the current from the alternator. Conventionally, a belt,direct or serpentine, couples an output shaft of the engine to thealternator to generate the AC power. Torque demands for generatingcurrent from the running engine are significantly lower than for enginestart-up. In order to appropriately transfer power between the engineand battery to both start the engine and generate electric power, anumber of different components and devices are typically required,thereby raising issues with respect to size, cost, and complexity.

SUMMARY OF THE DISCLOSURE

This disclosure provides a combined engine starter and electric powergenerator device with an integral transmission, such as may be used inwork vehicles for engine cold start and to generate electric power, thusserving the dual purposes of an engine starter and an alternator withmore robust power transmission to and from the engine in both cases.

In one aspect, the disclosure provides a combination starter-generatordevice for a work vehicle having an engine. The starter-generator deviceincludes an electric machine; a gear set configured to receiverotational input from the electric machine and from the engine and tocouple the electric machine and the engine in a first power flowdirection and a second power flow direction. The gear set is configuredto operate in one of at least a first gear ratio, a second gear ratio,or a third gear ratio in the first power flow direction and at least afourth gear ratio in the second power flow direction. Thestarter-generator device further includes a dog clutch arrangementselectively coupled to the gear set to effect the first, second, andthird gear ratios in the first power flow direction and the fourth gearratio in the second power flow direction.

In another aspect, the disclosure provides a drivetrain assembly for awork vehicle. The drivetrain assembly includes an engine; an electricmachine; and a gear set configured to receive rotational input from theelectric machine and from the engine and to couple the electric machineand the engine in a first power flow direction and a second power flowdirection. The gear set is configured to operate in one of at least afirst gear ratio, a second gear ratio, or a third gear ratio in thefirst power flow direction and at least the third gear ratio in thesecond power flow direction. The drivetrain assembly further includes adog clutch arrangement having at least a first clutch, a second clutch,and a third clutch selectively coupled to the gear set, each selectivelyrepositionable between an engaged position and a disengaged position.The first clutch, in the engaged position, is configured to effect thefirst gear ratio in the first power flow direction as a cold enginestart mode. The second clutch, in the engaged position, is configured toeffect the second gear ratio in the first power flow direction as a warmengine start mode. The third clutch, in the engaged position, isconfigured to effect the third gear ratio in the first power flowdirection as a boost mode and to effect the third gear ratio in thesecond power flow direction as a generation mode.

The details of one or more embodiments are set forth in the accompanyingdrawings and the description below. Other features and advantages willbecome apparent from the description, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side view of an example work vehicle in the formof an agricultural tractor in which the disclosed integratedstarter-generator device may be used;

FIG. 2 is a simplified partial isometric view of an engine of the workvehicle of FIG. 1 showing an example mounting location for an examplestarter-generator device;

FIG. 3 is a schematic diagram of a portion of a power transferarrangement of the work vehicle of FIG. 1 having an examplestarter-generator device;

FIG. 4 is an end isometric view of a power transmission assembly of theexample starter-generator device that may be implemented in the workvehicle of FIG. 1;

FIG. 5 is a cross-sectional view of a power transmission assembly of theexample starter-generator device that may be implemented in the workvehicle of FIG. 1;

FIG. 6 is a more detailed view of a portion of the power transmissionassembly of FIG. 5 for the example starter-generator device;

FIG. 7 is an isometric view of a cam plate that may be incorporated intothe power transmission assembly of FIG. 5 for the examplestarter-generator device;

FIG. 8 is an isometric view of clutches that may be incorporated intothe power transmission assembly of FIG. 5 for the examplestarter-generator device;

FIG. 9 is an isometric view of a stator plate that may be incorporatedinto the power transmission assembly of FIG. 5 for the examplestarter-generator device;

FIG. 10 is a sectional view of the power transmission assembly of FIG. 5depicting a schematic representation of a power flow path in a firstengine start mode of the example starter-generator device;

FIG. 11 is a sectional view of the power transmission assembly of FIG. 5depicting a schematic representation of a power flow path in a secondengine start mode of the example starter-generator device;

FIG. 12 is a sectional view of the power transmission assembly of FIG. 5depicting a schematic representation of a power flow path in a boostmode of the example starter-generator device;

FIG. 13 is a sectional view of the power transmission assembly of FIG. 5depicting a schematic representation of a power transfer path in ageneration mode of the example starter-generator device;

FIG. 14 is a partial sectional view of the power transmission assemblyof FIG. 5 in the first engine start mode of the examplestarter-generator device; and

FIG. 15 is a more detailed, partial view of a portion of the powertransmission assembly of FIG. 5 depicting a drag clutch of the examplestarter-generator device.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

The following describes one or more example embodiments of the disclosedstarter-generator device, as shown in the accompanying figures of thedrawings described briefly above. Various modifications to the exampleembodiments may be contemplated by one of skill in the art.

As used herein, unless otherwise limited or modified, lists withelements that are separated by conjunctive terms (e.g., “and”) and thatare also preceded by the phrase “one or more of” or “at least one of”indicate configurations or arrangements that potentially includeindividual elements of the list, or any combination thereof. Forexample, “at least one of A, B, and C” or “one or more of A, B, and C”indicates the possibilities of only A, only B, only C, or anycombination of two or more of A, B, and C (e.g., A and B; B and C; A andC; or A, B, and C).

As used herein, the term “axial” refers to a dimension that is generallyparallel to an axis of rotation, axis of symmetry, or centerline of acomponent or components. For example, in a cylinder or disc with acenterline and opposite, generally circular ends or faces, the “axial”dimension may refer to the dimension that generally extends in parallelto the centerline between the opposite ends or faces. In certaininstances, the term “axial” may be utilized with respect to componentsthat are not cylindrical (or otherwise radially symmetric). For example,the “axial” dimension for a rectangular housing containing a rotatingshaft may be viewed as a dimension that is generally in parallel withthe rotational axis of the shaft. Furthermore, the term “radially” asused herein may refer to a dimension or a relationship of componentswith respect to a line extending outward from a shared centerline, axis,or similar reference, for example in a plane of a cylinder or disc thatis perpendicular to the centerline or axis. In certain instances,components may be viewed as “radially” aligned even though one or bothof the components may not be cylindrical (or otherwise radiallysymmetric). Furthermore, the terms “axial” and “radial” (and anyderivatives) may encompass directional relationships that are other thanprecisely aligned with (e.g., oblique to) the true axial and radialdimensions, provided the relationship is predominately in the respectivenominal axial or radial dimension. Additionally, the term“circumferential” may refer to a collective tangential dimension that isperpendicular to the radial and axial dimensions about an axis.

Many conventional vehicle power systems include an internal combustionengine and/or one or more batteries (or other chemical power source)that power various components and subsystems of the vehicle. In certainelectric vehicles, a bank of batteries powers the entire vehicleincluding the drive wheels to impart motion to the vehicle. In hybridgas and electric vehicles, the motive force may alternate between engineand electric motor power, or the engine power may be supplemented byelectric motor power. In still other conventional vehicles, the electricpower system is used to initiate engine start up and to run thenon-drive electric systems of the vehicle. In the latter case, thevehicle typically has a starter motor that is powered by the vehiclebattery to turn the engine crankshaft to move the pistons within thecylinders. In further scenarios, the electric power system may provide aboost to an operating engine.

Some engines (e.g., diesel engines) initiate combustion by compressionof the fuel, while other engines rely on a spark generator (e.g., sparkplug), which is powered by the battery. Once the engine is operating ata sufficient speed, the power system may harvest the engine power topower the electric system as well as to charge the battery. Typically,this power harvesting is performed with an alternator or other type ofpower generator. The alternator converts alternating current (AC) powerto direct current (DC) power usable by the battery and vehicle electriccomponents by passing the AC power through an inverter (e.g., dioderectifier). Conventional alternators harness power from the engine bycoupling a rotor of the alternator to an output shaft of the engine (ora component coupled thereto). Historically this was accomplished by theuse of a dedicated belt, but in some more modern vehicles the alternatoris one of several devices that are coupled to (and thus powered by) theengine via a single “serpentine” belt.

In certain applications, such as in certain heavy-duty machinery andwork vehicles, it may be disadvantageous to have a conventional set-upwith separate starter and generator components. Such separate componentsrequire separate housings, which may require separate sealing orshielding from the work environment and/or occupy separate positionswithin the limited space of the engine compartment. Other enginecompartment layout complexities may arise as well.

The following describes one or more example implementations of animproved vehicle power system that addresses one or more of these (orother) matters with conventional systems. In one aspect, the disclosedsystem includes a combination or integrated device that performs theengine cranking function of a starter motor and the electric powergenerating function of a generator. The device is referred to herein asan integrated starter-generator device (“ISG” or “starter-generator”).This terminology is used herein, at least in some implementations of thesystem, to be agnostic to the type of power (i.e., AC or DC current)generated by the device. In some implementations, the starter-generatordevice may function to generate electricity in a manner of what personsof skill in the art may consider a “generator” device that produces DCcurrent directly. However, as used herein, the term “generator” shallmean producing electric power of static or alternating polarity (i.e.,AC or DC). Thus, in a special case of the starter-generator device, theelectric power generating functionality is akin to that of aconventional alternator, and it generates AC power that is subsequentlyrectified to DC power, either internally or externally to thestarter-generator device.

In certain embodiments, the starter-generator device may include adirect mechanical power coupling to the engine that avoids the use ofbelts between the engine and the starter-generator device. For example,the starter-generator device may include within its housing a powertransmission assembly with a gear set that directly couples to an outputshaft of the engine. The gear set may take any of various formsincluding arrangements with enmeshing spur or other gears as well asarrangements with one or more planetary gear sets. Large gear reductionratios may be achieved by the transmission assembly such that a singleelectric machine (i.e., motor or generator) may be used and operated atsuitable speeds for one or more types of engine start up, as well aselectric power generation. The direct power coupling between thestarter-generator device and engine may increase system reliability,cold starting performance, and electric power generation of the system.

Further, in certain embodiments, the starter-generator device may have apower transmission assembly that automatically and/or selectively shiftsgear ratios (i.e., shifts between power flow paths having different gearratios). By way of example, the transmission assembly may include one ormore engagement components that engage or disengage automatically orupon command. For example, passive engagement components, such as aone-way clutch (e.g., a roller or sprag clutch), may be used to effectpower transmission through a power flow path in the engine start updirection; and active engagement components, such as friction clutchassemblies, may be used to effect power transmission through other powerflow paths. In this manner, bi-directional or other clutch (or other)configurations may be employed to carry out the cranking and generatingfunctions with the appropriate control hardware. As a result of thebi-directional nature of the power transmission assembly, the powertransfer belt arrangement may be implemented with only a single belttensioner, thereby providing a relatively compact and simple assembly.In addition to providing torque in two different power flow directions,the gear set may also be configured and arranged to provide powertransmission from the electric machine to the engine at one of twodifferent speeds, e.g., according to different gear ratios. Theselection of speed may provide additional functionality and flexibilityfor the power transmission assembly.

In one example, the combination starter-generator may further include adog clutch arrangement with first, second, and third clutches that arering-shaped and concentrically arranged, each with clutch teeth thatselectively engage the gear set when the respective clutch isrepositioned from the disengaged position to the engaged position. Theclutches may be supported by a stator plate in between the clutches andthe gear set to accept reactive forces, thereby enabling some amount offlexibility of the clutches.

The combination starter-generator further includes a cam plate with camteeth that may be pivoted to force the clutches into the engagedpositions based on the angular position. The cam teeth that engage arespective clutch may be radially and circumferentially offset relativeto one another. In some examples, the clutches may include openings toaccommodate the cam teeth in the disengaged positions.

In some examples, the combination starter-generator clutch may furtherinclude a drag clutch that may be at least partially mounted on theinput shaft to slow the electric machine. The drag clutch may bepreloaded by a spring to create a predetermined amount of drag force,such as approximately 10 Nm. The drag force functions to facilitatesynchronization during speed or direction changes.

Each implementation will be discussed in greater detail below.

Referring to the drawings, an example work vehicle power system as adrivetrain assembly will be described in detail. As will become apparentfrom the discussion herein, the disclosed system may be usedadvantageously in a variety of settings and with a variety of machinery.For example, referring now to FIG. 1, the power system (or drivetrainassembly) 110 may be included in a work vehicle 100, which is depictedas an agricultural tractor. It will be understood, however, that otherconfigurations may be possible, including configurations with workvehicle 100 as a different kind of tractor, or as a work vehicle usedfor other aspects of the agriculture industry or for the constructionand forestry industries (e.g., a harvester, a log skidder, a motorgrader, and so on). It will further be understood that aspects of thepower system 110 may also be used in non-work vehicles and non-vehicleapplications (e.g., fixed-location installations).

Briefly, the work vehicle 100 has a main frame or chassis 102 supportedby ground-engaging wheels 104, at least the front wheels of which aresteerable. The chassis 102 supports the power system (or plant) 110 andan operator cabin 108 in which operator interface and controls (e.g.,various joysticks, switches levers, buttons, touchscreens, keyboards,speakers and microphones associated with a speech recognition system)are provided.

As schematically shown, the power system 110 includes an engine 120, anintegrated starter-generator device 130, a battery 140, and a controller150. The engine 120 may be an internal combustion engine or othersuitable power source that is suitably coupled to propel the workvehicle 100 via the wheels 104, either autonomously or based on commandsfrom an operator. The battery 140 may represent any one or more suitableenergy storage devices that may be used to provide electric power tovarious systems of the work vehicle 100.

The starter-generator device 130 couples the engine 120 to the battery140 such that the engine 120 and battery 140 may selectively interact inat least four modes. In a first (or cold engine start) mode, thestarter-generator device 130 converts electric power from the battery140 into mechanical power to drive the engine 120 at a relatively highspeed, e.g., during a relatively cold engine start up. In a second (orwarm engine start) mode, the starter-generator device 130 convertselectric power from the battery 140 into mechanical power to drive theengine 120 at a relatively low speed, e.g., during a relatively warmengine start up. In a third (or boost) mode, the starter-generatordevice 130 converts electric power from the battery 140 into mechanicalpower to drive the engine 120 to provide an engine boost. In a fourth(or generation) mode, the starter-generator device 130 convertsmechanical power from the engine 120 into electric power to charge thebattery 140. Additional details regarding operation of thestarter-generator device 130 during the engine start modes, the boostmode, and the generation mode are provided below.

As introduced above, the controller 150 may be considered part of thepower system 110 to control various aspects of the work vehicle 100,particularly characteristics of the power system 110. The controller 150may be a work vehicle electronic controller unit (ECU) or a dedicatedcontroller. In some embodiments, the controller 150 may be configured toreceive input commands and to interface with an operator via ahuman-machine interface or operator interface (not shown) and fromvarious sensors, units, and systems onboard or remote from the workvehicle 100; and in response, the controller 150 generates one or moretypes of commands for implementation by the power system 110 and/orvarious systems of work vehicle 100.

Generally, the controller 150 may be configured as computing deviceswith associated processor devices and memory architectures, ashydraulic, electrical or electro-hydraulic controllers, or otherwise. Assuch, the controller 150 may be configured to execute variouscomputational and control functionality with respect to the power system110 (and other machinery). The controller 150 may be in electronic,hydraulic, or other communication with various other systems or devicesof the work vehicle 100. For example, the controller 150 may be inelectronic or hydraulic communication with various actuators, sensors,and other devices within (or outside of) the work vehicle 100, includingvarious devices associated with the power system 110. Generally, thecontroller 150 generates the command signals based on operator input,operational conditions, and routines and/or schedules stored in thememory. For example, the operator may provide inputs to the controller150 via an operator input device that dictates the appropriate mode, orthat at least partially defines the operating conditions in which theappropriate mode is selected by the controller 150. In some examples,the controller 150 may additionally or alternatively operateautonomously without input from a human operator. The controller 150 maycommunicate with other systems or devices (including other controllers)in various known ways, including via a CAN bus (not shown), via wirelessor hydraulic communication means, or otherwise.

Additionally, power system 110 and/or work vehicle 100 may include ahydraulic system 152 with one or more electro-hydraulic control valves(e.g., solenoid valves) that facilitate hydraulic control of variousvehicle systems, particularly aspects of the starter-generator device130. The hydraulic system 152 may further include various pumps, lines,hoses, conduits, tanks, and the like. The hydraulic system 152 may beelectrically activated and controlled according to signals from thecontroller 150. In one example and as discussed in greater detail below,the hydraulic system 152 may be utilized to engage and/or disengageclutches within the starter-generator device 130, e.g., by applying andreleasing hydraulic pressure based on signals from the controller 150for one or more clutch actuators. Other mechanisms for controlling suchclutches may also be provided.

In one example, the starter-generator device 130 includes a powertransmission assembly (or transmission) 132, an electric machine ormotor 134, and an inverter/rectifier device 136, each of which may beoperated according to command signals from the controller 150. The powertransmission assembly 132 enables the starter-generator device 130 tointerface with the engine 120, particularly via a crank shaft (or anauxiliary drive shaft or other engine power transfer element) 122 of theengine 120. The power transmission assembly 132 may include one or moregear sets in various configurations to provide suitable power flows andgear reductions, as described below. The power transmission assembly 132variably interfaces with the electric machine 134 in two different powerflow directions such that the electric machine 134 operates as a motorduring the engine start and boost modes and as a generator during thegeneration mode. In one example, discussed below, the power transmissionassembly 132 is coupled to the electric machine 134 via a power transferbelt arrangement. This arrangement, along with the multiple gear ratiosprovided by the power transmission assembly 132, permits the electricmachine 134 to operate within optimal speed and torque ranges in bothpower flow directions. The inverter/rectifier device 136 enables thestarter-generator device 130 to interface with the battery 140, such asvia direct hardwiring or a vehicle power bus 142. In one example, theinverter/rectifier device 136 inverts DC power from the battery 140 intoAC power during the engine start modes and rectifies AC power to DCpower in the generation mode. In some embodiments, theinverter/rectifier device 136 may be a separate component instead ofbeing incorporated into the starter-generator device 130. Although notshown, the power system 110 may also include a suitable voltageregulator, either incorporated into the starter-generator device 130 oras a separate component.

Reference is briefly made to FIG. 2, which depicts a simplified partialisometric view of an example mounting location of the starter-generatordevice 130 relative to the engine 120. In this example, the integratedstarter-generator device 130 mounts directly and compactly to the engine120 so as not to project significantly from the engine 120 (and therebyenlarge the engine compartment space envelope) or interfere with variousplumbing lines and access points (e.g., oil tubes and fill opening andthe like). Notably, the starter-generator device 130 may generally bemounted on or near the engine 120 in a location suitable for coupling toan engine power transfer element (e.g., crank shaft 122 as introduced inFIG. 1).

Reference is additionally made to FIG. 3, which is a simplifiedschematic diagram of a power transfer belt arrangement 200 between thepower transmission assembly 132 and electric machine 134 of thestarter-generator device 130. It should be noted that FIGS. 2 and 3depict one example physical integration or layout configuration of thestarter-generator device 130. Other arrangements may be provided.

The power transmission assembly 132 is mounted to the engine 120 and maybe supported by a reaction plate 124. As shown, the power transmissionassembly 132 includes a first power transfer element 133 that isrotatably coupled to a suitable drive element of the engine 120 (e.g.,crank shaft 122 of FIG. 1) and a second power transfer element 135 inthe form of a shaft extending on an opposite side of the powertransmission assembly 132 from the first power transfer element 133.Similarly, the electric machine 134 is mounted on the engine 120 andincludes a further power transfer element 137.

The power transfer belt arrangement 200 includes a first pulley 210arranged on the second power transfer element 135 of the powertransmission assembly 132, a second pulley 220 arranged on the powertransfer element 137 of the electric machine 134, and a belt 230 thatrotatably couples the first pulley 210 to the second pulley 220 forcollective rotation. As described in greater detail below, during theengine start modes, the electric machine 134 pulls the belt 230 torotate pullies 210, 220 in a first clock direction D1 to drive the powertransmission assembly 132 (and thus the engine 120); during the boostmode, the electric machine 134 pulls the belt 230 to rotate pullies 210,220 in a second clock direction D2 to drive the power transmissionassembly 132 (and thus the engine 120); and during the generation mode,the power transmission assembly 132 enables the engine 120 to pull thebelt 230 and rotate pullies 210, 220 in the second clock direction D2 todrive the electric machine 134.

As a result of the bi-directional configuration, the power transfer beltarrangement 200 may include only a single belt tensioner 240 to applytension to a single side of the belt 230 in both directions D1, D2.Using a single belt tensioner 240 to tension the belt 230 isadvantageous in that it reduces parts and complexity in comparison to adesign that requires multiple belt tensioners. As described below, thebi-directional configuration and associated simplified power transferbelt arrangement 200 are enabled by the bi-directional nature of thegear set in the power transmission assembly 132. Additionally, adifference in the circumferences of the first and second pullies 210,220 provides a change in the gear ratio between the power transmissionassembly 132 and the electric machine 134. In one example, the powertransfer belt arrangement 200 may provide a gear ratio of between3:1-5:1, particularly a 4:1 ratio.

In one example, FIG. 4 depicts an engine-side isometric view of thepower transmission assembly 132 that may be implemented into thestarter-generator device 130. As shown, the power transmission assembly132 includes a housing 302 with a rotatable housing element 303 that, inthis example, functions as a power transfer element of the assembly 132and engages a corresponding power transfer element (e.g., crank shaft122) of the engine 120. A stationary housing mount 304 supports thehousing 302 on the engine 120 (not shown in FIG. 4). In this example,the housing mount 304 includes three support legs with first ends thatextend from the side of the housing 302 opposite the engine 120 andsecond ends that mount to the engine 120 (not shown in FIG. 4).

The power transmission assembly 132 is additionally depicted in thecross-sectional view of FIG. 5. As shown, the power transmissionassembly 132 may be considered to be a unit with the annular housing 302configured to house various components of the power transmissionassembly 132. In the view of FIG. 5, a first side 306 of the powertransmission assembly 132 is oriented towards the electric machine 134,and a second side 308 of the power transmission assembly 132 is orientedtowards the engine 120. As shown, the housing 302 further includes astationary housing element 305 positioned in between the rotatablehousing element 303 and the housing mount 304. The housing mount 304 andstationary housing element 305 are positioned relative to the rotatablehousing element 303 on bearings 307 that enable the relative rotationduring operation.

At the first side 306, the power transmission assembly 132 includes aninput shaft 310 that is coupled to the electric machine 134 (e.g., viathe power transfer belt arrangement 200). In some examples, the inputshaft 310 may be directly connected to the power transfer element 135described above with reference to FIGS. 1 and 2; and in furtherexamples, the input shaft 310 may be coupled through intermediatecomponents, such as a flange or boss. It should be noted that, althoughthe shaft 310 is described as an “input” shaft, it may transfer powerboth into and out of the power transmission assembly 132, depending onthe mode, as described below. The input shaft 310 generally extendsthrough the power transmission assembly 132 to define a primary axis ofrotation 300.

The power transmission assembly 132 generally includes a planetary gearset 320. As described below, the planetary gear set 320 is a two stageplanetary gear set and generally enables the power transmission assembly132 to interface with the electric machine 134 (e.g., via the powertransfer belt arrangement 200) and the engine 120 (e.g., via directcoupling to the crank shaft 122 of the engine 120). In some embodiments,the input shaft 310 may be considered part of the planetary gear set320. Although one example configuration of the planetary gear set 320 isdescribed below, other embodiments may have different configurations.

Reference is additionally made to FIG. 6, which is a closer view of aportion of FIG. 5. The planetary gear set 320 includes a first-stage sungear 322 mounted for rotation on the input shaft 310. The first-stagesun gear 322 includes a plurality of teeth or splines that mesh with aset of first-stage planet gears 324 that circumscribe the first-stagesun gear 322. In one example, the first-stage planet gears 324 include asingle circumferential row of one or more planet gears, although otherembodiments may include radially stacked rows, each with an odd numberof planet gears.

The first-stage planet gears 324 are supported by a first-stage planetcarrier 326, which circumscribes the first-stage sun gear 322, as wellas the input shaft 310, and is at least partially formed by first andsecond radially extending, axially facing carrier plates 328, 330. Thefirst-stage carrier plates 328, 330 include a row of mounting locationsfor receiving axles extending through and supporting the first-stageplanet gears 324 for rotation. As such, in this arrangement, each of theplanet axles respectively forms an individual axis of rotation for eachof the first-stage planet gears 324, and the first-stage planet carrier326 enables the set of first-stage planet gears 324 to collectivelyrotate about the first-stage sun gear 322.

The gear set 320 further includes a ring gear 332 that circumscribes thefirst-stage sun gear 322 and the first-stage planet gears 324. The ringgear 332 includes radially interior teeth that engage the teeth of thefirst-stage planet gears 324. As such, first-stage planet gears 324extend between, and engage with, the first-stage sun gear 322 and thering gear 332. In some embodiments, a ring gear cover 333 may be mountedwithin the interior of the ring gear 332 The ring gear cover 333functions to at least partially enclose the gear set 320 within thehousing 302.

In effect, the ring gear 332 is integral with the rotatable housingelement 303, which as noted above is positioned on bearings 307 torotate relative to the stationary housing mount 304. With respect to theplanetary gear set 320, the ring gear 332 may function as the powertransfer element 133 relative to the engine 120. In particular, the ringgear 332 includes a number of castellations 336 that extend axiallyabout the circumference of the axial face that faces the engine 120. Thecastellations 336 engage and rotatably fix the ring gear 332 to thecrank shaft 122 of the engine 120. The ring gear 332 may be consideredan output element of the power transmission assembly 132; however,similar to the input shaft 310, the ring gear 332 may receive rotationalinput in both power flow directions.

The gear set 320 further includes a second-stage sun gear 340 that isgenerally hollow and cylindrical, extending between first and secondends 342, 344, and circumscribing the input shaft 310. The first-stageplanet carrier 326 has a splined engagement with, or is otherwise fixedto, the second-stage sun gear 340 proximate to the first end 342.Additionally, the second-stage sun gear 340 may include a series ofsplines that mesh with a set of second-stage planet gears 346. Thesecond-stage planet gears 346 are supported by a second-stage planetcarrier 348 formed by first and second planet carrier plates 350, 352.The second-stage planet gears 346 are positioned to additionally engagewith the ring gear 332. The second-stage planet gears 346 each have anaxle that extends between the two carrier plates 350, 352 that enableeach planet gear 346 to rotate relative to the planet carrier 348 aboutthe respective axle. As such, the second-stage planet gears 346 arepositioned in between, and engage with each of, the second-stage sungear 340 and the ring gear 332. In some examples, each second-stageplanet gear 346 has a different number of teeth than each correspondingfirst-stage planet gear 324, while in other examples, each second-stageplanet gear 346 has the same number of teeth as each correspondingfirst-stage planet gear 328.

As will now be described in greater detail, the power transmissionassembly 132 additionally includes a clutch arrangement 360 configuredto selectively engage and disengage various components of the planetarygear set 320 to modify the power flow through the power transmissionassembly 132.

Generally, the clutch arrangement 360 includes a cam actuator or plate370, an actuator assembly 380, a first (or low) clutch 390, a second (ormid) clutch 400, a third (or high) clutch 410, and a stator plate 420.As described below, each clutch 390, 400, 410 may be shifted between anengaged position and a disengaged position. As such, the clutches 390,400, 410 may be considered “shifting” clutches that are activelyactuated to modify power flow within the power transmission assembly132.

In one example, the actuator assembly 380 operates to pivot the camplate 370, which in turn, selectively moves the clutches 390, 400, 410with support of the stator plate 420 into engagement with the gear set320 from the disengaged positions to the engaged positions. Although notshown, one or more springs may be provided to maintain the position ofthe clutches 390, 400, 410 when not in engaged positions and/or returnthe clutches 390, 400, 410 to the disengaged positions upon subsequentrepositioning of the cam plate 370. For example, a first spring (notshown) is positioned in between the low clutch 390 and the stator plate420, a second spring (not shown) is positioned in between the mid clutch400 and the stator plate 420, and a third spring (not shown) ispositioned in between the high clutch 410 and the stator plate 420 tobias the clutches 390, 400, 410 away from the stator plate 420 in thedisengaged positions. In effect, each of the clutches 390, 400, 410operates as a “cam actuated, spring released” arrangement. In someexamples, the clutch arrangement 360 may further include a drag clutch440 that also impacts the power flow through the power transmissionassembly 132. As described in greater detail below after a discussion ofthe other aspects of the clutch arrangement 360, the drag clutch 440 maybe considered a passive clutch.

As schematically shown, the gear set 320 includes a number of engagementelements 430, 432, 434 that enable interaction between variouscomponents of the gear set 320 and the clutches 390, 400, 410.Generally, the engagement elements 430, 432, 434 are configured asslots, locks, or pockets that interact with the clutches 390, 400, 410,as described below. In some examples, one or more of the engagementelements 430, 432, 434 may be bi-directional with two angled walls ortwo perpendicular walls, or one or more of the engagement elements 430,432, 434 may be designed having a single orientation, e.g., having anangled wall opposing a perpendicular wall.

The first engagement elements 430 may be in the form of one or moreslots or locks on the second-stage planet carrier 348. The firstengagement elements 430 operate to receive a portion of the low clutch390, as discussed below, to lock the second-stage planet carrier 348 toa stationary housing element 305, i.e., to ground the second-stageplanet carrier 348 and prevent rotation.

The second engagement elements 432 may be in the form of one or moreslots or locks on the second-stage sun gear 340. The second engagementelements 432 operate to receive a portion of the mid clutch 400, asdiscussed below, to lock the second-stage sun gear 340 to the stationaryhousing element 305, i.e., to ground the second-stage sun gear 340 andprevent rotation.

The third engagement elements 434 are configured to selectively coupleand decouple the first-stage sun gear 322 and to the second-stage sungear 340 via the input shaft 310. In one example, the third engagementelements 434 include one or more shifting or sliding elements that arerepositionable between a first position that enables independentrotation of the second-stage sun gear 340 relative to the input shaft310 (which is rotationally coupled to the first-stage sun gear 322) anda second position that connects the second-stage sun gear 340 for mutualrotation with the input shaft 310 (and thus the first-stage sun gear322). As discussed in greater detail below, actuation of the high clutch410 into the engaged position shifts the third engagement elements 434into the second position such that the second-stage sun gear 340 islocked to the first-stage sun gear 322 via the input shaft 310. As thehigh clutch 410 is returned to the disengaged position, the thirdengagement elements 434 are returned to the first position (e.g., with aspring) such that the second-stage sun gear 340 is decoupled from thefirst-stage sun gear 322 and the input shaft 310.

Reference is briefly made to FIG. 7, which is an isometric view of thecam plate 370 removed from the power transmission assembly 132. Asshown, the cam plate 370 is generally disc or ring shaped, with a firstface 371 and second face 372 that define an outer circumference 374 andan center mounting aperture 375. The cam plate 370 is mounted within thepower transfer assembly 132 and configured to pivot through anappropriate range, e.g., approximately 30°, about an axis coaxial to theprimary axis of rotation 300. The cam plate 370 includes a series of camteeth 376, 377, 378 at designated circumferential and radial positionsto selectively interact with the clutches 390, 400, 410 in the axialdirection, depending on the angular position of the cam plate 370. Inthis example, the cam teeth 376, 377, 378 include a first row of camteeth 376 in a first circumferential row at a common radial distancethat interact with the low clutch 390; a second row of cam teeth 377 ina second circumferential row at a common radial distance that interactwith the mid clutch 400; and in a third circumferential row at a commonradial distance that interact with the high clutch 410. As shown, therows of cam teeth 376, 377, 378 have individual circumferentialpositions relative to the other rows of teeth 376, 377, 378. In otherwords, the cam teeth 376, 377, 378 in individual rows are radiallyoffset from the cam teeth 376, 377, 378 of other rows. In this manner,the cam plate 370 may be positioned to selectively engage individualclutches 390, 400, 410, as described in greater detail below. In someexamples, each tooth 376, 377, 378 may have a shape that facilitatesengagement and disengagement with the respective clutches 390, 400, 410.For example, each tooth 376, 377, 378 may have one angled side and onegenerally perpendicular side relative to the face 371 of the cam plate370. The angled side provides a smoother movement, particularly duringdisengagement. Moreover, each of the cam teeth 376, 377, 378 may have arelatively flat top surface that provides a greater surface forengagement with the clutches 390, 400, 410, described below.

Briefly, referring again to FIG. 6, the cam plate 370 may be pivoted bythe actuator assembly 380. In one example, the actuator assembly 380includes a flange 382 extending from the second face 372 of the camplate 370 and terminating in a piston element 384 that is positionedwithin a cylinder element 386. The cylinder element 386 of the actuatorassembly 380 is arranged in the stationary housing element 305 proximateto the housing mount 304 and is fluidly coupled to a hydraulic circuit(not shown) having a source of hydraulic fluid, control valves, pumps,and the like operatively coupled to the controller 150. By modifying thefluid pressure in the cylinder element 386, the piston element 384 isrepositioned, which in turn functions to reposition the cam plate 370.Accordingly, the actuator assembly 380 may be controlled by modifyingthe fluid pressure in the cylinder element 386 via the hydraulic circuitbased on commands from the controller 150. In this manner, thecontroller 150 may command the position of the cam plate 370 toimplement the desired mode of operation. Other types of actuatorassemblies may be provided to reposition the cam plate 370, includinglinear actuators.

Reference is now made to FIG. 8, which is an isometric view of theclutches 390, 400, 410 removed from the power transmission assembly 132.In one example, the clutches 390, 400, 410 may be considered “dog” typeclutches. As shown, the clutches 390, 400, 410 are generally configuredas concentric rings. The low clutch 390 is the largest and is formed byfirst and second faces 391, 392 and outer and inner circumferences 393,394 that define a clutch ring base 395. The mid clutch 400 is positionedin between the low clutch 390 and the high clutch 410, and the midclutch 400 is formed by first and second faces 401, 402 and outer andinner circumferences 403, 404 that define a clutch ring base 405. Thehigh clutch 410 is the smallest, arranged radially inside the mid clutch400, and is formed by first and second faces 411, 412 and outer andinner circumferences 413, 414 that define a clutch ring base 415.Collectively, the clutches 390, 400, 410 may be mounted on a spindleextending from the stationary housing element 305 and configured toindividually move axially but remain stationary in the circumferentialand radial dimensions.

Each clutch 390, 400, 410 further defines a series of clutch teeth 396,406, 416 that extend generally perpendicularly from the respective firstclutch face 391, 401, 411 of the ring base 395, 405, 415 and clutchopenings 397, 407, 417 of the ring base 395, 405, 415, eachcircumferentially adjacent a respective one of the clutch teeth 396,406, 416. In this embodiment, four clutch teeth 396, 406, 416 and fourclutch openings 397, 407, 417 are provided for each clutch 390, 400,410. Other embodiments may have greater or fewer number of teeth and/oropenings. The clutch teeth 396, 406, 416 may have a slight ramp orangled shape at the intersection of the respective tooth 396, 406, 416and base 395, 405, 415 that assists in engagement and disengagement ofthe clutch 390, 400, 410.

In one embodiment, each of the clutches 390, 400, 410 may be formed froma single plate of material that undergoes stamping to form the clutchteeth 396, 406, 416 and clutch openings 397, 407, 417. As described ingreater detail below, the stamping process enables a dog-type clutch390, 400, 410 in which 1) the clutch teeth 396, 406, 416 are configuredto engage the gear set 320; 2) the shape of the teeth 396, 406, 416provides a ramp that facilitates engagement; 3) the openings 397, 407,417 enable clearance for the cam plate 370 when disengaged; and 4) thestructure of each clutch 390, 400, 410 enables load sharing duringoperation.

In this example, the clutch teeth 396 and clutch openings 397 of the lowclutch 390 are generally radially aligned with corresponding clutchteeth 406 and clutch openings 407 of the mid clutch 400, which in turnare generally radially aligned with corresponding clutch teeth 416 andclutch openings 417 of the high clutch 410. As described below, theclutches 390, 400, 410 are supported such that the clutches 390, 400,410 may have some amount of flexibility to accommodate relative movementwithin the power transmission assembly 132.

As noted above, the clutches 390, 400, 410 are generally arrangedconcentrically and are rotationally stationary. However, each clutch390, 400, 410 is arranged to shift axially, out of the concentricarrangement, from a disengaged position into an engaged position by thecam plate 370, and subsequently back into the disengaged positions. Inthe engaged positions, the clutch teeth 396, 406, 416 of the shiftedclutch 390, 400, 410 selectively engage the gear set 320. In otherwords, the cam plate 370 has angular positions in which the cam teeth376, 377, 378 are accommodated by the clutch openings 397, 407, 417corresponding to disengaged clutch positions and other angular positionsin which the cam teeth 376, 377, 378 contact the respective second face392, 402, 412 of the selected clutch 390, 400, 410 to force therespective clutch 390, 400, 410 axially into an engaged position suchthat the corresponding clutch teeth 396, 406, 416 engage with theengagement elements 430, 432, 434 of the gear set 320 to modify powerflow. Additional details and examples of operation will be providedbelow.

Reference is now made to FIG. 9, which is an isometric view of thestator plate 420 removed from the power transmission assembly 132. Thestator plate 420 is generally disc shaped with a first face 421 orientedtowards the gear set 320 and a second face 422 oriented towards theclutches 390, 400, 410. The stator plate 420 defines a number of slots424, 425, 426 in rows at designated radial and circumferentialpositions. In particular, the stator plate 420 includes a firstcircumferential row of slots 424 that are positioned to accommodate theclutch teeth 396 of the low clutch 390 when the low clutch 390 is in theengaged position; a second circumferential row of slots 425 that arepositioned to accommodate the clutch teeth 406 of the mid clutch 400when the mid clutch 400 is in the engaged position; and a thirdcircumferential row of slots 426 that are positioned to accommodate theclutch teeth 416 of the high clutch 410 when the high clutch 410 is inthe engaged position. During operation, the stator plate 420 isstationary without rotational or axial movement. As described in greaterdetail below, the stator plate 420 functions to accept the reactiveloads resulting from the engagements between the clutches 390, 400, 410and the engagement elements 430, 432, 434 of the gear set 320. This alsoenables the clutches 390, 400, 410 to have some amount of flexibility.

As introduced above, the power transmission assembly 132 may be operatedto selectively function in one of four different modes, including: afirst or low engine start mode in which the power transmission assembly132 transfers power from the battery 140 to the engine 120 with a firstgear ratio; a second or warm engine start mode in which the powertransmission assembly 132 transfers power from the battery 140 to theengine 120 with a second gear ratio; a third or boost mode in which thepower transmission assembly 132 transfers power from the battery 140 tothe engine 120 with a third gear ratio; and a generation mode in whichthe power transmission assembly 132 transfers power from the engine 120to the battery 140 in a fourth gear ratio, which in this example isequal to the third gear ratio. Comparatively, the engine start modes arerelatively low speed and relatively high torque output, and the boostand generation modes are relatively high speed and relatively low torqueoutput. As such, the power transmission assembly 132 and the powertransfer belt arrangement 200 are bi-directional and have differentgearing ratios to transfer power in different power flow directions andalong different power flow paths, depending on the mode. The power flowpaths in the different modes are described below with reference to FIGS.10-13 in which arrows are provided to schematically represent the flowsof power.

Reference is now made to FIG. 10, which is a depiction of the powertransmission assembly 132 in the cold engine start mode, annotated witharrows representing the power flow path. In the discussion below,reference is additionally made to FIGS. 7-9, as well as FIG. 14, whichis a sectional view of a portion of the power transmission assembly 132in the cold engine start mode.

In this example, the actuator assembly 380, commanded by the controller150, functions to pivot the cam plate 370 into a first angular position.In this position, the first cam teeth 376 of the cam plate 370 engagethe second face 392 of the low clutch 390 to move the low clutch 390into the engaged position. Also in the first angular position, thesecond cam teeth 377 of the cam plate 370 are accommodated within theopenings 407 of the mid clutch 400 and the third cam teeth 378 of thecam plate 370 are accommodated within the openings 417 of the highclutch 410, thereby resulting in the mid clutch 400 and the high clutch410 remaining in the disengaged positions. Since the first cam teeth 376of the cam plate 370 engage the second face 392 of the low clutch 390,the low clutch 390 is pressed axially towards the gear set 320. As thelow clutch 390 is pressed in this direction, the clutch teeth 396 of thelow clutch 390 extend through the first slots 424 in the stator plate420 and into the first engagement elements 430 on the second-stageplanet carrier 348, thereby resulting in the engaged position of the lowclutch 390. In the disengaged positions, the clutch teeth 406 of the midclutch 400 and the clutch teeth 416 of the high clutch 410 may at leastpartially be positioned within the slots 425, 426 of the stator plate420, although in some embodiments, the clutch teeth 406, 416 ofdisengaged clutches 400, 410 may remain completely outside of the statorplate 420.

The positioning of the clutch teeth 396 through the stator plate 420into the first engagement elements 430 of the second-stage planetcarrier 348 functions to ground and prevent rotation of the second-stageplanet carrier 348. In this position, the stator plate 420 supports thelow clutch 390 by receiving the reaction forces from the second-stageplanet carrier 348. The view of FIG. 14 particularly depicts the camteeth 376 of the cam plate 370 axially shifting the low clutch 390 suchthat the clutch teeth 396 extend through the slots 424 of the statorplate 420 and into the engagement elements 430 of the second-stageplanet carrier 348. Although not visible in FIG. 14, the cam teeth 377,378 of the cam plate 370 are accommodated by the openings 407, 417 inthe mid and high clutches 400, 410 such that these clutches 400, 410remain disengaged.

As the second-stage planet carrier 348 is grounded, the powertransmission assembly 132 may operate in the cold engine start mode. Inthe cold engine start mode, the engine 120 may be initially inactive,and activation of the ignition by an operator in the cabin 108 of thework vehicle 100 energizes the electric machine 134 to operate as amotor. In particular and additionally referring to FIG. 3, the electricmachine 134 rotates the pulley 220 in the first clock direction D1,thereby driving the belt 230 and pulley 210 in the first clock directionD1. The pulley 210 drives the element 135, and thus the input shaft 310,in the first clock direction D1. Rotation of the input shaft 310 drivesrotation of the first-stage sun gear 322, and in turn, rotation of thefirst-stage sun gear 322 drives rotation of the first-stage planet gears324. The first-stage planet gears 324 drive the first-stage planetcarrier 326, which as noted above is splined with the second-stage sungear 340. As a result, the first-stage planet carrier 326 drives thesecond-stage sun gear 340 and thus the second-stage planet gears 346. Asnoted above, the second-stage planet carrier 348 is grounded by the lowclutch 390. As such, rotation of the first-stage and second-stage planetgears 324, 346 operates to drive the ring gear 332. Since the number offirst-stage and second-stage planet gears 324, 346 in the power flowpath is an odd number (e.g., 1) in the radial direction, the first-stageand second-stage planet gears 324, 346 drive the ring gear 332 in theopposite direction (e.g., the second clock direction D2) relative to thefirst-stage and second-stage sun gear 322, 340 rotating in the firstclock direction D1. As noted above, the ring gear 332 functions as thepower transfer element 133 to interface with the crank shaft 122 of theengine 120 to drive and facilitate engine start. In effect, during thecold engine start mode, the power transmission assembly 132 operates asa sun-in, ring-out configuration.

In one example, the power transmission assembly 132 provides a 15:1 gearratio in the power flow direction of the cold engine start mode. Inother embodiments, other gear ratios (e.g., 10:1-30:1) may be provided.Considering a 4:1 gear ratio from the power transfer belt arrangement200, a resulting 60:1 gear ratio (e.g., approximately 40:1 to about120:1) may be achieved for the starter-generator device 130 between theelectric machine 134 and the engine 120 during the cold engine startmode. As such, if for example the electric machine 134 is rotating at10,000 RPM, the crank shaft 122 of the engine 120 rotates at about100-150 RPM. In one example, the power transmission assembly 132 maydeliver a torque of approximately 3000 Nm to the engine 120.Accordingly, the electric machine 134 may thus have normal operatingspeeds with relatively lower speed and higher torque output for coldengine start up.

Reference is now made to FIG. 11, which is a partial cross-sectionalview of the power transmission assembly 132 similar to that of FIG. 5annotated with power flow arrows. The power flow arrows of FIG. 11particularly depict operation of the power transmission assembly 132 inthe warm engine start mode

In this example, the actuator assembly 380, commanded by the controller150, functions to pivot the cam plate 370 into a second angularposition. In this position, the second cam teeth 377 of the cam plate370 engage the second face 402 of the mid clutch 400 to place the midclutch 400 in the engaged position. Also in the second angular position,the first cam teeth 376 of the cam plate 370 are accommodated within theopenings 397 of the low clutch 390 and the third cam teeth 378 of thecam plate 370 are accommodated within the openings 417 of the highclutch 410, thereby resulting in the low clutch 390 and the high clutch410 remaining in the disengaged positions. Since the second cam teeth377 of the cam plate 370 engage the second face 402 of the mid clutch400, the mid clutch 400 is pressed towards the gear set 320. As the midclutch 400 is pressed in this direction, the clutch teeth 406 of the midclutch 400 extend through the second slots 425 in the stator plate 420and into the second engagement elements 432 on the second-stage sun gear340, thereby resulting in the engaged position of the mid clutch 400. Inthe disengaged positions, the clutch teeth 396 of the low clutch 390 andthe clutch teeth 416 of the high clutch 410 may at least partially bepositioned within the slots 424, 426 of the stator plate 420, althoughin some embodiments, the clutch teeth 396, 416 of disengaged clutches390, 410 may remain completely outside of the stator plate 420.

The positioning of the clutch teeth 406 of the mid clutch 400 throughthe stator plate 420 into the second engagement elements 432 of thesecond-stage sun gear 340 functions to ground and prevent rotation ofthe second-stage sun gear 340. In this position, the stator plate 420functions to receive the reaction forces from the second-stage sun gear340. Additionally, since the first-stage planet carrier 326 is splinedto the second-stage sun gear 340, engagement of the mid clutch 400 alsooperates to ground the first-stage planet carrier 326.

In the warm engine start mode, the engine 120 may be initially inactiveor active. In any event, the controller 150 energizes the electricmachine 134 to operate as a motor. In particular and additionallyreferring to FIG. 3, the electric machine 134 rotates the pulley 220 inthe first clock direction D1, thereby driving the belt 230 and pulley210 in the first clock direction D1. The pulley 210 drives the element135, and thus the input shaft 310, in the first clock direction D1.

Since the first-stage sun gear 322 is mounted on the input shaft 310,rotation of the input shaft 310 also rotates the first-stage sun gear322. In turn, rotation of the first-stage sun gear 322 drives rotationof the first-stage planet gears 324. Since the first-stage planetcarrier 326 and second-stage sun gear 340 are grounded, rotation of thefirst-stage planet gears 324 drives rotation of the ring gear 332.

Since the number of first-stage planet gears 324 in the power flow pathis an odd number (e.g., 1) in the radial direction, the first-stageplanet gears 324 drive the ring gear 332 in the opposite direction(e.g., the second clock direction D2) relative to the input shaft 310and the first-stage sun gear 322 rotating in the first clock directionD1. As noted above, the ring gear 332 functions as the power transferelement 133 to interface with the crank shaft 122 of the engine 120 todrive and facilitate engine start. In effect, during the warm enginestart mode, the power transmission assembly 132 operates as a sun-in,ring-out configuration, albeit at a lower gear ratio as compared to thecold engine start mode resulting from using the ratio of thesecond-stage planet gears 346 as opposed to the compounded ratio of thefirst- and second-stage planet gears 324, 346.

In one example, the power transmission assembly 132 provides a 4:1 gearratio in the power flow direction of the warm engine start mode. Inother embodiments, other gear ratios (e.g., 3:1-7:1) may be provided.Considering a 4:1 gear ratio from the power transfer belt arrangement200, a resulting 16:1 gear ratio (e.g., approximately 12:1 to about28:1) may be achieved for the starter-generator device 130 between theelectric machine 134 and the engine 120 during the warm engine startmode. As such, if for example the electric machine 134 is rotating at10,000 RPM, the crank shaft 122 of the engine 120 rotates at about600-700 RPM. In one example, the torque output of the power transmissionassembly 132 for the engine 120 is approximately 400-600 Nm.Accordingly, the electric machine 134 may thus have normal operatingspeeds with a relatively lower speed and higher torque output for enginestart up or boost.

Reference is made to FIG. 12, which is a partial sectionalcross-sectional view of the power transmission assembly 132 similar tothat of FIG. 5 annotated with power flow arrows. The power flow arrowsof FIG. 12 particularly depict operation of the power transmissionassembly 132 in the boost mode.

In this example, the actuator assembly 380, commanded by the controller150, functions to pivot the cam plate 370 into a third angular position.In this position, the third cam teeth 378 of the cam plate 370 engagethe second face 412 of the high clutch 410 to place the high clutch 410in the engaged position. Also in the third angular position, the firstcam teeth 376 of the cam plate 370 are accommodated within the openings397 of the low clutch 390 and the second cam teeth 377 of the cam plate370 are accommodated within the openings 407 of the mid clutch 400,thereby resulting in the low clutch 390 and the mid clutch 400 remainingin the disengaged positions. Since the third cam teeth 378 of the camplate 370 engage the second face 412 of the high clutch 410, the highclutch 410 is pressed towards the gear set 320. As the high clutch 410is pressed in this direction, the clutch teeth 416 of the high clutch410 extend through the third slots 426 in the stator plate 420 and intothe third engagement elements 434, thereby resulting in the engagedposition of the high clutch 410. As noted above, engagement of the thirdengagement elements 434 by the high clutch 410 functions to lock thesecond-stage sun gear 340 to the first-stage sun gear 322. In thedisengaged positions, the clutch teeth 396 of the low clutch 390 and theclutch teeth 406 of the mid clutch 400 may at least partially bepositioned within the slots 424, 425 of the stator plate 420, althoughin some embodiments, the clutch teeth 396, 406 of disengaged clutches390, 400 may remain completely outside of the stator plate 420.

As the second-stage sun gear 340 and the first-stage sun gear 322 arelocked for collective rotation, the power transmission assembly 132 mayoperate in the boost mode. In the boost mode, the engine 120 may beinitially active and the controller 150 energizes the electric machine134 to operate as a motor. In particular and additionally referring toFIG. 3, the electric machine 134 rotates the pulley 220 in the secondclock direction D2, thereby driving the belt 230 and pulley 210 in thesecond clock direction D2. The pulley 210 drives the element 135, andthus the input shaft 310, in the second clock direction D2. Rotation ofthe input shaft 310 drives rotation of the first-stage sun gear 322, andin turn, rotation of the first-stage sun gear 322 drives rotation of thesecond-stage sun gear 340, thereby resulting in the first-stage sun gear322, the second-stage sun gear 340, first-stage planet carrier 326,first-stage planet gears 324, second-stage planet carrier 348, andsecond-stage planet gears 346 rotating as a unit about the rotationalaxis 300 with the input shaft 310 to drive the ring gear 332. Since theother components of the planetary gear set 320 rotate with the inputshaft 310, the ring gear 332 is driven in the same second clockdirection D2. As noted above, the ring gear 332 functions as the powertransfer element 133 to interface with the crank shaft 122 of the engine120 to drive the engine 120. In effect, during the boost mode, the powertransmission assembly 132 operates as a sun-in, ring-out configuration.

In one example, the power transmission assembly 132 provides a 1:1 gearratio in the power flow direction of the boost mode. In otherembodiments, other gear ratios may be provided. Considering a 4:1 gearratio from the power transfer belt arrangement 200, a resulting 4:1 gearratio may be achieved for the starter-generator device 130 between theelectric machine 134 and the engine 120 during the boost mode. As such,if for example the electric machine 134 is rotating at 10,000 RPM, thecrank shaft 122 of the engine 120 rotates at about 2500 RPM.Accordingly, the electric machine 134 may thus have normal operatingspeeds while providing an appropriate boost speed to the engine 120.

Reference is made to FIG. 13, which is a cross-sectional view of thepower transmission assembly 132 similar to that of FIG. 5 annotated withpower flow arrows. The power flow arrows of FIG. 13 particularly depictoperation of the power transmission assembly 132 in the generation mode

In this example, the actuator assembly 380, commanded by the controller150, functions to pivot the cam plate 370 into the third angularposition. As noted above, in this position, the third cam teeth 378 ofthe cam plate 370 engage the second face 412 of the high clutch 410,such that the high clutch 410 is engaged and the low and mid clutches390, 400 are disengaged. As the high clutch 410 is engaged, the clutchteeth 416 of the high clutch 410 extend through the third slots 426 inthe stator plate 420 and into the third engagement elements 434, and thethird engagement elements 434 function to lock the second-stage sun gear340 to the first-stage sun gear 322.

As the second-stage sun gear 340 and the first-stage sun gear 322 arelocked for collective rotation, the power transmission assembly 132 mayoperate in the generation mode. Subsequent to the engine start modesand/or the boost mode, the engine 120 begins to accelerate aboverotational speed provided by power transmission assembly 132, and theelectric machine 134 is commanded to decelerate and to cease providingtorque to power transmission assembly 132. After the engine 120 hasstabilized to a sufficient speed and the electric machine 134 hassufficiently decelerated or stopped, the high clutch 410 is engaged asdescribed above to operate the power transmission assembly 132 in thegeneration mode.

In the generation mode, the engine 120 rotates the crank shaft 122 andpower transfer element 133 that is engaged with the ring gear 332, thusdriving the ring gear 332 in the second clock direction D2. The ringgear 332 drives the first-stage planet gears 324 and the second-stageplanet gears 346, which respectively drive the first-stage sun gear 322and the second-stage sun gear 340.

Since the first-stage sun gear 322 is engaged to the second-stage sungear 340, the rotations of the first-stage and second-stage sun gears322, 340 are transferred to the input shaft 310. Therefore, as the ringgear 332 rotates in the second clock direction D2, the input shaft 310is driven and similarly rotates in the second clock direction D2 at thesame rate of rotation. As noted above, the input shaft 310 is connectedwith and provides output power to the electric machine 134 in the secondclock direction D2 via the power transfer belt arrangement 200. Ineffect, during the generation mode, the power transmission assembly 132operates as a ring-in, sun-out configuration

In one example, the power transmission assembly 132 provides a 1:1 gearratio in the power flow direction of the generation mode. In otherembodiments, other gear ratios may be provided. Considering a 4:1 gearratio from the power transfer belt arrangement 200, a resulting 4:1 gearratio may be achieved for the starter-generator device 130 between theelectric machine 134 and the engine 120 during the generation mode. As aresult, the electric machine 134 may thus have normal operating speedsin both power flow directions with relatively low torque output duringpower generation.

As will now be described, the power transmission assembly 132 mayfurther be configured to facilitate transitions between the modes,particularly by slowing down the electric machine 134. Reference is nowmade to FIG. 15, which is a closer, more detailed view of a portion ofFIG. 5 according to one example. The view in FIG. 15 particularlydepicts a drag or synchronizing clutch 440. As shown, the drag clutch440 is positioned in between the input shaft 310 and the ring gear cover333 mounted to the ring gear 332. In particular, the drag clutch 440includes a shaft plate 446 mounted on the input shaft 310 that rotateswith the input shaft 310. The drag clutch 440 further includes one ormore cover plates 444, parallel to one another, that are mounted on thering gear cover 333. In this example, the shaft plate 446 is mounted inbetween the cover plates 444. A spring (schematically shown) 448 may beprovided to urge the cover plates 444 and the shaft plate 446 togethersuch that the plates 444, 446 have a frictional engagement. Thisfrictional engagement creates a drag force between the input shaft 310and the ring gear 332 (and thus, (and thus, between the electric machine132 and the engine 120).

Since the electric machine 132 is typically moving at a higher speedthan the engine 120, the drag clutch 440 generally operates to reducethe speed of the electric machine 132 relative to the engine 120 toenable synchronization. This facilitates the transitions between themodes, particularly between the cold engine start mode and the warmengine start mode, between the warm engine start mode and the boostmode, and between the boost mode and generation mode.

The frictional engagement between the plates 444, 446 of the drag clutch440 (particularly, the force of the spring 448) may be preset or“preloaded” with a designated amount of force, as necessary or desiredto provide the appropriate amount of drag. An example drag force may be,for example, 10 Nm, although other drag force amounts may be provided.In one embodiment, the engagement of the clutches 390, 400, 410 with thegear set 320 may result in the gear set 320 pressing against the dragclutch 440, thereby increasing the drag force to further decrease motorspeed and facilitating faster transitions.

Thus, various embodiments of the vehicle electric system have beendescribed that include an integrated starter-generator device. Varioustransmission assemblies may be included in the device, thus reducing thespace occupied by the system. The transmission assembly may providemultiple speeds or gear ratios and transition between speeds/gearratios. One or more clutch arrangements may be used to selectively applytorque to the gear set of the transmission assembly in both power flowdirections. Direct mechanical engagement with the engine shaft reducesthe complexity and improves reliability of the system. Using planetarygear sets in the transmission assembly provides high gear reduction andtorque capabilities with reduced backlash in a compact space envelope.As a result of the bi-directional nature of the power transmissionassembly, the power transfer belt arrangement may be implemented withonly a single belt tensioner, thereby providing a relatively compact andsimple assembly. Additionally, by using the power transfer beltarrangement with belt and pullies to couple together and transfer powerbetween the electric machine and the power transmission assembly,instead of directly connecting and coupling the electric machine to thepower transmission assembly, the electric machine may be mounted apartfrom the transmission assembly to better fit the engine in a vehicleengine bay. Additionally, by using the belt and pullies to couple theelectric machine to the power transmission assembly, an additional gearratio (e.g., a 4:1 ratio) may be achieved. Embodiments discussed aboveinclude a double planetary gear set, sun in, ring out configuration toprovide warm and cold engine start modes and a ring in, sun outconfiguration to provide a generation mode. As such, a four modeassembly may be provided.

As noted above, the dog clutch arrangement provides clutches with someamount of flexibility to modify the power flow paths in a relativelycompact and robust assembly. The cam arrangement cooperates with the dogclutch arrangement to reposition the clutches from disengaged positionsto engaged positions based on the angular position in a reliable andrelatively simple manner. In some examples, the combinationstarter-generator clutch may further include a drag clutch thatfunctions to facilitate synchronization during speed or directionchanges.

Also, the following examples are provided, which are numbered for easierreference.

1. A combination starter-generator device for a work vehicle having anengine, the starter-generator device comprising: an electric machine; agear set configured to receive rotational input from the electricmachine and from the engine and to couple the electric machine and theengine in a first power flow direction and a second power flowdirection, the gear set configured to operate in one of at least a firstgear ratio, a second gear ratio, or a third gear ratio in the firstpower flow direction and at least a fourth gear ratio in the secondpower flow direction; and a dog clutch arrangement selectively coupledto the gear set to effect the first, second, and third gear ratios inthe first power flow direction and the fourth gear ratio in the secondpower flow direction.

2. The combination starter-generator device of example 1, wherein thedog clutch arrangement includes at least a first clutch and a secondclutch, each selectively repositionable between an engaged position anda disengaged position, and wherein the first and second clutches arering-shaped with the second clutch concentrically arranged within thefirst clutch when both of the first and second clutches are in thedisengaged positions.

3. The combination starter-generator device of example 2, wherein thefirst clutch includes a first ring base and at least one first clutchtooth extending from the first ring base and the second clutch includesa second ring base and at least one second clutch tooth extending fromthe second ring base.

4. The combination starter-generator device of example 3, wherein the atleast one first clutch tooth is engaged with the gear set to effect thefirst gear ratio when the first clutch is in the engaged position and isdisengaged from the gear set when the first clutch is in the disengagedposition, and wherein the at least one second clutch tooth is engagedwith the gear set to effect the second gear ratio when the second clutchis in the engaged position and is disengaged from the gear set when thesecond clutch is in the disengaged position.

5. The combination starter-generator device of example 4, wherein thedog clutch arrangement further includes a third clutch, alsorepositionable between the engaged position and the disengaged position,with a third ring base and at least one third clutch tooth extendingfrom the third ring base, the third clutch being concentrically arrangedwithin the second clutch when both of the second and third clutches arein the disengaged positions, and wherein the at least one third clutchtooth is engaged with the gear set when the third clutch is in theengaged position and is disengaged from the gear set when the thirdclutch is in the disengaged position.

6. The combination starter-generator device of example 5, wherein thedog clutch arrangement further includes a stator plate axially inbetween the gear set and the first, second, and third clutches when thefirst, second, and third clutches are in the disengaged positions,wherein the stator plate defines at least one first slot, at least onesecond slot, and at least one third slot, and wherein the at least onefirst slot receives the at least one first clutch tooth when the firstclutch is in the engaged position, the at least one second slot receivesthe at least one second clutch tooth when the second clutch is in theengaged position, wherein the at least one third slot receives the atleast one third clutch tooth when the third clutch is in the engagedposition.

7. The combination starter-generator device of example 6, furthercomprising a spring arrangement positioned in between the first clutch,the second clutch, and the third clutch and the stator plate andconfigured to selectively move the first clutch, the second clutch, andthe third clutch from the engaged positions into the disengagedpositions.

8. The combination starter-generator device of example 6, furthercomprising a cam actuator configured to selectively move the firstclutch, the second clutch, and the third clutch from the disengagedpositions into the engaged positions.

9. The combination starter-generator device of example 8, wherein thefirst clutch includes at least one first opening, the second clutchincludes at least one second opening, and the third clutch includes atleast one third opening, and wherein the at least one first opening, theat least one second opening, and the at least one third opening areconfigured to accommodate the cam actuator when the first, second, andthird clutches are respectively in the disengaged positions.

10. The combination starter-generator device of example 9, wherein theat least one first opening is immediately adjacent the at least onefirst clutch tooth, the at least one second opening is immediatelyadjacent the at least one second clutch tooth, and at least one thirdopening is immediately adjacent the at least one third clutch tooth.

11. The combination starter-generator device of example 10, wherein thefirst clutch is formed by a stamping process to form the at least onefirst tooth and the at least one first opening.

12. The combination starter-generator device of example 9, wherein thegear set includes a compound epicyclic gear train including an inputshaft, first-stage and second-stage sun gears, first-stage andsecond-stage planet gears, first-stage and second-stage carriers, and aring gear with the first-stage planet carrier splined to thesecond-stage sun gear, and wherein the first-stage planet gears have adifferent gear tooth count than the second-stage planet gears; wherein,in a cold engine start mode, the first clutch is in the engaged positionto ground the second-stage planet carrier and the second and thirdclutches are in the disengaged positions, and further, rotational powerfrom the electric machine moves in the first power flow direction fromthe input shaft, to the first-stage sun gear, to the first stage-planetgears, to the first-stage planet carrier, to the second-stage sun gear,to the second-stage planet gears, and to the ring gear out to the engineat the first gear ratio; and wherein, in a warm engine start mode, thesecond clutch is in the engaged position to ground the second-stage sungear and the first and third clutches are in the disengaged positions,and further, the rotational power from the electric machine moves in thefirst power flow direction from the input shaft, to the first-stage sungear, to the first stage-planet gears, and to the ring gear out to theengine at the second gear ratio.

13. The combination starter-generator device of example 12, wherein, ina boost mode, the third clutch is in the engaged position to couple thesecond-stage sun gear to the first-stage sun gear and the first andsecond clutches are in the disengaged positions, and further, therotational power from the electric machine moves in the first power flowdirection from the input shaft, to the first-stage and second-stage sungears, to the first-stage and second-stage planet gears, and to the ringgear out to the engine at the third gear ratio; and wherein, in ageneration mode, the third clutch is in the engaged position to couplethe second-stage sun gear to the first-stage sun gear and the first andsecond clutches are in the disengaged positions, and further, rotationalpower from the engine moves in the second power flow direction from thering gear, to the first-stage and second-stage planet gears, to thefirst-stage and second-stage sun gears, and to the input shaft out tothe electric machine at the fourth gear ratio.

14. The combination starter-generator device of example 13, wherein eachof the third gear ratio and the fourth gear ratio is a 1:1 ratio throughthe gear set.

15. The combination starter-generator device of example 14, wherein thefirst gear ratio is greater than the second gear ratio, and the secondgear ratio is greater than the third gear ratio.

As will be appreciated by one skilled in the art, certain aspects of thedisclosed subject matter can be embodied as a method, system (e.g., awork vehicle control system included in a work vehicle), or computerprogram product. Accordingly, certain embodiments can be implementedentirely as hardware, entirely as software (including firmware, residentsoftware, micro-code, etc.) or as a combination of software and hardware(and other) aspects. Furthermore, certain embodiments can take the formof a computer program product on a computer-usable storage medium havingcomputer-usable program code embodied in the medium.

Any suitable computer usable or computer readable medium can beutilized. The computer usable medium can be a computer readable signalmedium or a computer readable storage medium. A computer-usable, orcomputer-readable, storage medium (including a storage device associatedwith a computing device or client electronic device) can be, forexample, but is not limited to, an electronic, magnetic, optical,electromagnetic, infrared, or semiconductor system, apparatus, ordevice, or any suitable combination of the foregoing. More specificexamples (a non-exhaustive list) of the computer-readable medium wouldinclude the following: an electrical connection having one or morewires, a portable computer diskette, a hard disk, a random-access memory(RAM), a read-only memory (ROM), an erasable programmable read-onlymemory (EPROM or Flash memory), an optical fiber, a portable compactdisc read-only memory (CD-ROM), an optical storage device. In thecontext of this document, a computer-usable, or computer-readable,storage medium can be any tangible medium that can contain, or store aprogram for use by or in connection with the instruction executionsystem, apparatus, or device.

A computer readable signal medium can include a propagated data signalwith computer readable program code embodied therein, for example, inbaseband or as part of a carrier wave. Such a propagated signal can takeany of a variety of forms, including, but not limited to,electro-magnetic, optical, or any suitable combination thereof. Acomputer readable signal medium can be non-transitory and can be anycomputer readable medium that is not a computer readable storage mediumand that can communicate, propagate, or transport a program for use byor in connection with an instruction execution system, apparatus, ordevice.

Aspects of certain embodiments are described herein can be describedwith reference to flowchart illustrations and/or block diagrams ofmethods, apparatus (systems) and computer program products according toembodiments of the disclosure. It will be understood that each block ofany such flowchart illustrations and/or block diagrams, and combinationsof blocks in such flowchart illustrations and/or block diagrams, can beimplemented by computer program instructions. These computer programinstructions can be provided to a processor of a general purposecomputer, special purpose computer, or other programmable dataprocessing apparatus to produce a machine, such that the instructions,which execute via the processor of the computer or other programmabledata processing apparatus, create means for implementing thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

These computer program instructions can also be stored in acomputer-readable memory that can direct a computer or otherprogrammable data processing apparatus to function in a particularmanner, such that the instructions stored in the computer-readablememory produce an article of manufacture including instructions whichimplement the function/act specified in the flowchart and/or blockdiagram block or blocks.

The computer program instructions can also be loaded onto a computer orother programmable data processing apparatus to cause a series ofoperational steps to be performed on the computer or other programmableapparatus to produce a computer implemented process such that theinstructions which execute on the computer or other programmableapparatus provide steps for implementing the functions/acts specified inthe flowchart and/or block diagram block or blocks.

Any flowchart and block diagrams in the figures, or similar discussionabove, can illustrate the architecture, functionality, and operation ofpossible implementations of systems, methods and computer programproducts according to various embodiments of the present disclosure. Inthis regard, each block in the flowchart or block diagrams can representa module, segment, or portion of code, which includes one or moreexecutable instructions for implementing the specified logicalfunction(s). It should also be noted that, in some alternativeimplementations, the functions noted in the block (or otherwisedescribed herein) can occur out of the order noted in the figures. Forexample, two blocks shown in succession (or two operations described insuccession) can, in fact, be executed substantially concurrently, or theblocks (or operations) can sometimes be executed in the reverse order,depending upon the functionality involved. It will also be noted thateach block of any block diagram and/or flowchart illustration, andcombinations of blocks in any block diagrams and/or flowchartillustrations, can be implemented by special purpose hardware-basedsystems that perform the specified functions or acts, or combinations ofspecial purpose hardware and computer instructions.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the disclosure.As used herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

The description of the present disclosure has been presented forpurposes of illustration and description, but is not intended to beexhaustive or limited to the disclosure in the form disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of thedisclosure. Explicitly referenced embodiments herein were chosen anddescribed in order to best explain the principles of the disclosure andtheir practical application, and to enable others of ordinary skill inthe art to understand the disclosure and recognize many alternatives,modifications, and variations on the described example(s). Accordingly,various embodiments and implementations other than those explicitlydescribed are within the scope of the following claims.

What is claimed is:
 1. A combination starter-generator device for a work vehicle having an engine, the starter-generator device comprising: an electric machine; a gear set configured to receive rotational input from the electric machine and from the engine and to couple the electric machine and the engine in a first power flow direction and a second power flow direction, the gear set configured to operate in one of at least a first gear ratio, a second gear ratio, or a third gear ratio in the first power flow direction and at least a fourth gear ratio in the second power flow direction; and a dog clutch arrangement selectively coupled to the gear set to effect the first, second, and third gear ratios in the first power flow direction and the fourth gear ratio in the second power flow direction.
 2. The combination starter-generator device of claim 1, wherein the dog clutch arrangement includes at least a first clutch and a second clutch, each selectively repositionable between an engaged position and a disengaged position, and wherein the first and second clutches are ring-shaped with the second clutch concentrically arranged within the first clutch when both of the first and second clutches are in the disengaged positions.
 3. The combination starter-generator device of claim 2, wherein the first clutch includes a first ring base and at least one first clutch tooth extending from the first ring base and the second clutch includes a second ring base and at least one second clutch tooth extending from the second ring base.
 4. The combination starter-generator device of claim 3, wherein the at least one first clutch tooth is engaged with the gear set to effect the first gear ratio when the first clutch is in the engaged position and is disengaged from the gear set when the first clutch is in the disengaged position, and wherein the at least one second clutch tooth is engaged with the gear set to effect the second gear ratio when the second clutch is in the engaged position and is disengaged from the gear set when the second clutch is in the disengaged position.
 5. The combination starter-generator device of claim 4, wherein the dog clutch arrangement further includes a third clutch, also repositionable between the engaged position and the disengaged position, with a third ring base and at least one third clutch tooth extending from the third ring base, the third clutch being concentrically arranged within the second clutch when both of the second and third clutches are in the disengaged positions, and wherein the at least one third clutch tooth is engaged with the gear set when the third clutch is in the engaged position and is disengaged from the gear set when the third clutch is in the disengaged position.
 6. The combination starter-generator device of claim 5, wherein the dog clutch arrangement further includes a stator plate axially in between the gear set and the first, second, and third clutches when the first, second, and third clutches are in the disengaged positions, wherein the stator plate defines at least one first slot, at least one second slot, and at least one third slot, and wherein the at least one first slot receives the at least one first clutch tooth when the first clutch is in the engaged position, the at least one second slot receives the at least one second clutch tooth when the second clutch is in the engaged position, wherein the at least one third slot receives the at least one third clutch tooth when the third clutch is in the engaged position.
 7. The combination starter-generator device of claim 6, further comprising a spring arrangement positioned in between the first clutch, the second clutch, and the third clutch and the stator plate and configured to selectively move the first clutch, the second clutch, and the third clutch from the engaged positions into the disengaged positions.
 8. The combination starter-generator device of claim 6, further comprising a cam actuator configured to selectively move the first clutch, the second clutch, and the third clutch from the disengaged positions into the engaged positions.
 9. The combination starter-generator device of claim 8, wherein the first clutch includes at least one first opening, the second clutch includes at least one second opening, and the third clutch includes at least one third opening, and wherein the at least one first opening, the at least one second opening, and the at least one third opening are configured to accommodate the cam actuator when the first, second, and third clutches are respectively in the disengaged positions.
 10. The combination starter-generator device of claim 9, wherein the at least one first opening is immediately adjacent the at least one first clutch tooth, the at least one second opening is immediately adjacent the at least one second clutch tooth, and at least one third opening is immediately adjacent the at least one third clutch tooth.
 11. The combination starter-generator device of claim 10, wherein the first clutch is formed by a stamping process to form the at least one first tooth and the at least one first opening.
 12. The combination starter-generator device of claim 9, wherein the gear set includes a compound epicyclic gear train including an input shaft, first-stage and second-stage sun gears, first-stage and second-stage planet gears, first-stage and second-stage carriers, and a ring gear with the first-stage planet carrier splined to the second-stage sun gear, and wherein the first-stage planet gears have a different gear tooth count than the second-stage planet gears; wherein, in a cold engine start mode, the first clutch is in the engaged position to ground the second-stage planet carrier and the second and third clutches are in the disengaged positions, and further, rotational power from the electric machine moves in the first power flow direction from the input shaft, to the first-stage sun gear, to the first stage-planet gears, to the first-stage planet carrier, to the second-stage sun gear, to the second-stage planet gears, and to the ring gear out to the engine at the first gear ratio; and wherein, in a warm engine start mode, the second clutch is in the engaged position to ground the second-stage sun gear and the first and third clutches are in the disengaged positions, and further, the rotational power from the electric machine moves in the first power flow direction from the input shaft, to the first-stage sun gear, to the first stage-planet gears, and to the ring gear out to the engine at the second gear ratio.
 13. The combination starter-generator device of claim 12, wherein, in a boost mode, the third clutch is in the engaged position to couple the second-stage sun gear to the first-stage sun gear and the first and second clutches are in the disengaged positions, and further, the rotational power from the electric machine moves in the first power flow direction from the input shaft, to the first-stage and second-stage sun gears, to the first-stage and second-stage planet gears, and to the ring gear out to the engine at the third gear ratio; and wherein, in a generation mode, the third clutch is in the engaged position to couple the second-stage sun gear to the first-stage sun gear and the first and second clutches are in the disengaged positions, and further, rotational power from the engine moves in the second power flow direction from the ring gear, to the first-stage and second-stage planet gears, to the first-stage and second-stage sun gears, and to the input shaft out to the electric machine at the fourth gear ratio.
 14. The combination starter-generator device of claim 13, wherein each of the third gear ratio and the fourth gear ratio is a 1:1 ratio through the gear set.
 15. The combination starter-generator device of claim 14, wherein the first gear ratio is greater than the second gear ratio, and the second gear ratio is greater than the third gear ratio.
 16. A drivetrain assembly for a work vehicle, comprising: an engine; an electric machine; a gear set configured to receive rotational input from the electric machine and from the engine and to couple the electric machine and the engine in a first power flow direction and a second power flow direction, the gear set configured to operate in one of at least a first gear ratio, a second gear ratio, or a third gear ratio in the first power flow direction and at least the third gear ratio in the second power flow direction; and a dog clutch arrangement having at least a first clutch, a second clutch, and a third clutch selectively coupled to the gear set, each selectively repositionable between an engaged position and a disengaged position, wherein the first clutch, in the engaged position, is configured to effect the first gear ratio in the first power flow direction as a cold engine start mode, wherein the second clutch, in the engaged position, is configured to effect the second gear ratio in the first power flow direction as a warm engine start mode, wherein the third clutch, in the engaged position, is configured to effect the third gear ratio in the first power flow direction as a boost mode and to effect the third gear ratio in the second power flow direction as a generation mode.
 17. The drivetrain assembly of claim 16, further including a belt and pulley coupled to the gear set and the electric machine, wherein input power in the first power flow direction is conveyed from the electric machine to the gear set by the belt and pulley, and wherein in the first power flow direction the belt and pulley rotate in the first clock direction and in the second power flow direction the belt and pulley rotate in the second clock direction.
 18. The drivetrain assembly of claim 17, wherein the third clutch is concentrically arranged within the second clutch when the second and third clutches are in the disengaged positions, and wherein the second clutch is concentrically arranged within the first clutch when the first and second clutches are in the disengaged positions, wherein the first clutch includes a first ring base and at least one first clutch tooth extending from the first ring base, the second clutch includes a second ring base and at least one second clutch tooth extending from the second ring base, and the third clutch includes a third ring base and at least one third clutch tooth extending from the third ring base, wherein the dog clutch arrangement further includes a stator plate axially in between the gear set and the first, second, and third clutches when the first, second, and third clutches are in the disengaged positions, and wherein the stator plate defines at least one first slot, at least one second slot, and at least one third slot, the at least one first slot receiving the at least one first clutch tooth when the first clutch is in the engaged position, the at least one second slot receiving the at least one second clutch tooth when the second clutch is in the engaged position, the at least one third slot receiving the at least one third clutch tooth when the third clutch is in the engaged position.
 19. The drivetrain assembly of claim 18, further comprising a cam actuator configured to selectively move the first clutch, the second clutch, and the third clutch from the disengaged positions into the engaged positions, wherein the first clutch includes at least one first opening, the second clutch includes at least one second opening, and the third clutch includes at least one third opening, and wherein the at least one first, second, and third openings are configured to accommodate the cam actuator when the first, second, and third clutches are respectively in the disengaged positions.
 20. The drivetrain assembly of claim 19, wherein the gear set includes a compound epicyclic gear train including an input shaft, first-stage and second-stage sun gears, first-stage and second-stage planet gears, first-stage and second-stage carriers, and a ring gear with the first-stage planet carrier splined to the second-stage sun gear, and wherein the first-stage planet gears have a different gear tooth count than the second-stage planet gears; wherein, in the cold engine start mode, the first clutch is in the engaged position to ground the second-stage planet carrier and the second and third clutches are in the disengaged positions, and further, rotational power from the electric machine moves in the first power flow direction from the input shaft, to the first-stage sun gear, to the first stage-planet gears, to the first-stage planet carrier, to the second-stage sun gear, to the second-stage planet gears, and to the ring gear out to the engine at the first gear ratio; wherein, in the warm engine start mode, the second clutch is in the engaged position to ground the second-stage sun gear and the first and third clutches are in the disengaged positions, and further, the rotational power from the electric machine moves in the first power flow direction from the input shaft, to the first-stage sun gear, to the first stage-planet gears, and to the ring gear out to the engine at the second gear ratio; wherein, in the boost mode, the third clutch is in the engaged position to couple the second-stage sun gear to the first-stage sun gear and the first and second clutches are in the disengaged positions, and further, the rotational power from the electric machine moves in the first power flow direction from the input shaft, to the first-stage and second-stage sun gears, to the first-stage and second-stage planet gears, and to the ring gear out to the engine at the third gear ratio; and wherein, in the generation mode, the third clutch is in the engaged position to couple the second-stage sun gear to the first-stage sun gear and the first and second clutches are in the disengaged positions, and further, rotational power from the engine moves in the second power flow direction from the ring gear, to the first-stage and second-stage planet gears, to the first-stage and second-stage sun gears, and to the input shaft out to the electric machine at the third gear ratio. 